Certain lysosomal enzymes have recognition sites associated covalently with the enzyme molecules which mediate their binding and uptake into cells. The recognition site is carbohydrate in nature and appears to contain N-acetyl-glucosamine. Other forms of lysosomal enzymes (e.g. normal serum Beta-glucuronidase) are not taken up and lack the appropriate recognition site. The proposed work is the elucidation of molecular mechanism by which cells take up lysosomal enzymes and macromolecules.